Method of making a chromatographic element containing a resinous binder and product produced thereby



Dec. 24, 1968 w. J. STAUDENMAYER ET AL 3,418,152

METHOD OF MAKING A CHROMATOGRAPHIC ELEMENT CQNTAINING A RESINOUS BINDERAND PRODUCT PRODUCED THEREBY I Filed Aug. 1, 1966 HROMATOGRAPHICALLYACTIVE LAYER F 3 fliflnvenfion) 9 8 g 7 H v g: 4 A (prior art) LU I {I 3E R 2 2 I 5 4 5 TIME IN MINUTES WILLIAM J- STAUDENMAYER EDMOND S- PERRYUnited States Patent 3,418,152 METHOD OF MAKING A CHROMATOGRAPHICELEMENT CONTAINING A RESINOUS BINDER AND PRODUCT PRODUCED THEREBYWilliam Joseph Staudenmayer and Edmond S. Perry, Rochester, N.Y.,assignors to Eastman Kodak Company, Rochester, N.Y., a corporation ofNew Jersey Continuation-impart of application Ser. No. 450,362, Apr. 23,1965. This application Aug. 1, 1966, Ser. No. 569,441

Claims. (Cl. 117-63) ABSTRACT OF THE DISCLOSURE A thin-layerchromatographic element made by coating on an inert support a dispersionof particulate finely-divided chromatographically-active adsorbent andparticulate resinous binder in a liquid dispersing medium, removing thedispersing medium, and softening the particles of resinous binder torender them adherent and thereby form a continuous, coherent, porouslayer. The support can be utilized as a permanent part of thechromatographic element or the coated layer can be stripped from thesupport and used as a self-supporting layer.

This application is a continuation-in-part of our US. patent applicationSer. No. 450,362, filed Apr. 23, 1965, entitled, Chromatographic Sheets.

This invention relates to new chromatographic sheets for thin-layerchromatography and methods of making them; in one of its aspects itrelates to a highly coherent chromatographic layer of excellentporosity, which can be self-supporting or bonded to a support which doesnot react with or absorb the developer (eluting solvent) or modify thechromatographic separation of the porous layer.

Thin-layer chromatographic techniques heretofore known in the art arebecoming increasingly popular in analytical chemistry. Advantagesinclude simplicity, speed, and applicability to a wide variety ofseparations. The large number of adsorbents available and ease ofintroducing other components such as fiuorescing or complexing agents orvarying conditions such as eluting solvents present a number ofparameters which may be manipulated to obtain the desired separation.

One major shortcoming stands in the way of more widespread acceptance ofthin-layer chromatography: the tragility and abrasion propensity of suchprior art thin-layer chromatographic elements. Conventionalchromatographic elements comprise a glass plate bearing a thin layer ofloosely adherent adsorbent powder. They are available commercially butsince such preformed layers are fragile they are very prone to damagefrom the handling incident to packaging and shipping. Furthermore, theyare inconvenient to store and generally unsuitable for record purposesbecause of their susceptibility to abrasion and breakage. Consequentlythe plates are more often coated by the user when he needs them.

It is an object of this invention to provide light, flexible, thin-layerchromatographic sheets which have the handling ease of a sheet ofordinary paper and which have outstanding resistance to abrasion.

It is another object to provide such chromatographic sheets which can betreated with alkaline eluting solvents without loss in quality of theresultant record.

It is another object .to provide such flexible thin-layerchromatographic sheets which can withstand chemical or oxidativecharring as by sulfuric acid charring and provide an archival-qualityrecord, without any detriment to the chromatographic and handlingproperties.

ICC

It is another object to provide firmly bonded, thick, highly adsorbent,chromatographic layers of high porosity and good flexibility forpreparative-scale chromatograph- 1c separation.

It is still another object to provide a method of preparing thin-layerchromatographic sheets which insures that the sheets will demonstrateexcellent abrasion resistance, that the thin adsorbent layer will have ahigh degree of porosity, and that the adsorbent will retain its abilityto adsorb chemicals.

It is a further object of this invention to provide strongly coherent,porous, flexible chromatographic layers which can be optionallyself-supporting, loosely adherent to a temporary support, or stronglyadherent to a permanent support.

Other objects of this invention will be apparent from the drawing andthe following detailed disclosure.

The invention comprises a thin-layer chromatographic recording materialhaving a continuous, coherent, porous layer of finely divided, discreteparticles of chromatographic adsorbent bonded to associated particles ofa resinous binder. In order not to impair the chromatographic activityof the adsorbent the quantity of binder is held low enough so as not tocoat the chromatographic particles nor to completely fill the voidsbetween the particles and the binder material. The binder particlesadhere to portions of the surfaces of adjacent adsorbent particles tobind the chromatographic particles together in a layer of goodmechanical strength. They also provide adhesion to the base when asupported layer is desired.

Coatings made according to the present invention are microscopicallyheterogeneous, particulate and porous. Under magnified viewingconditions, they present a sintered or spongelike appearance. Typicallythe layers of our invention are prepared by coating a dispersion of amixture of fine particles of adsorbent and suitable resin binder,removing the liquid dispersing medium and then softening the resinsufliciently to insure adhesion to adjoining adsorbent particles andoptionally to a support, by means of heat, pressure, solvent or thelike.

The unique method of preparing the layer permits preparation of strongcoherent, porous-layer coatings with chromatographic capacity of thesame high order as that of binder-free prior art coatings. Since thelayers of this invention are coherent, flexible and abrasion-resistant,it is not necessary to use glass plates or other rigid supports toprovide strength and protection for the conventional chromatographiccoatings. A flexible inert support can be employed or the porouschromatographic layer can be employed without a separate support.

If it was considered desirable to put these new porous layers on glass,it would be an improvement over the prior systems as the chromatographiclayer can be precoated and handled in a routine manner without damagingit. :It also can be retained as permanent record.

Thin-layer chromatography is a separation technique having widespreadutility with numerous unknowns and solvents. Since organic solvents arecustomarily employed in thin-layer chromatography, illustration of thisinvention will be p imarily concerned with binders which function in thedesired manner with such solvents. However, this invention is equallyapplicable to less commonly used chromatographic elutants includingaqueous liquids.

Typical thin-layer chromatographic elements have adsorbent layers about10 mils thick. However, it is also an integral part of this invention toprovide thicker chromatographic layers up to about 40 mils in thicknessto facilitate the separation of larger amounts of single com pound.Previous attempts to make such thicker layers have generally resulted incoatings which break up even with very careful handling. With the newtechniques for preparation disclosed in this invention and the fusedparticullate type of porous binder employed, we have successfullyprepared thick chromatographic layers for use in the separation ofrelatively large amounts of material.

Until now, it has been impossible to obtain a visualized chromatographicseparation which could withstand normal handling without abrading ordestroying part of the record.

In the chromatographic separation of colorless compounds a techniquecalled visualization is used. This consists of, e.g. sulfuric acidcharring or similar treatment to show the chromatographic separation.The visualization of chromatograms by acid charring techniques isdisclosed in the book, Thin-Layer Chromatography, by James M. Bobbit,and published by the Reinhold Publishing Corporation, New York, 1963,pages 85-86.

The thin-layer chromatographic layers of the present invention areconventionally coated on inert supports chosen so as not to affect thechromatographic activity of of the adsorbent. With our strongly coherentlayers, a support is not necessary except as a temporary measure inpreparing the initial coating. If desired after the coherent layer hasbeen prepared, the temporary support can be stripped away. Where apermanent support is desired, the chromatographic layers of ourinvention can be coated on many surfaces and advantageously on plasticfilms, e.g., polyolefins, polyesters, olyolefin-subbed polyesters,polyamides, polycarbonates, cellulose esters, or on plastic coatedpaper, on aluminum or other metal films, or on glass. Polyolefin coatedpapers are especially attractive; they are much less expensive than anequivalent thickness of the polyolefin.

Our invention is not limited with respect to the adsorbent used. Anyparticulate adsorbent can be used such as alumina, silica gel,kieselguhr, polyamide, cellulose, etc. Advantageously, the particlesshould be fine enough to pass through a U.S. Standard 325 mesh screen.Additives such as phosphorescent or fluorescent compounds, and otherswhich have been employed in prior art thinlayer chromatographic elementsmay be incorporated. These include calcium silicate, calciummetasilicate, and zinc silicate.

Separatory procedures in which currently available binder-free glassplate chromatographic elements have been used are facilitated by the useof the layers of our invention. Thus silver nitrate is frequentlyincorporated in the adsorbent layer to form weak complexes with olefinicgroups to differentiate these materials. When silver nitrate is usedwith the binder-free elements of the prior art, it is added to theslurry of adsorbent prior to coating. This renders the already fragilepowdery adsorbent coating even more fragile. However, the elements ofour invention need merely be dipped into an alcoholic silver nitratesolution and dried prior to use. The treated elements retain theirexcellent coherence and abrasion resistance.

While it is not essential, the chromatographic elements of our inventioncan be activated in a known manner by heating before use. Our elementsrespond to such activation in substantially the same way as do thebinderfree, thin-layer chromatographic elements showing substantiallythe same degree of improvement after heating for about one hour at 110C. This further illustrates that the chromatographic properties of ourlayers do not suffer from the presence of a particulate binder which sogreatly improves the mechanical properties of the material.

A wide choice of resinous binders is available which can be used infinely divided, particulate form to make the strong, highly adsorbentlayers of our invention.

The resinous powder becomes tacky by application of heat, pressure orsolvents or some combination of these. The particle size of theadsorbent and the resin, the ratio of adsorbent to resin, the selectionof slurrying and coat ing vehicle and the degree of softening of theresin in the treatment after coating to prodpcg the desired layercoherence are all important and may be varied depending on particularconditions of use.

Typically a volume of powdered resin binder which is 10 per-cent to 50percent of the volume of the chromatographic adsorbent, producesadvantageous results although other ranges may be useful with particularcombinations of adsorbent and resin.

The slurrying and coating vehicle is typically a liquid which is neithera solvent for, nor chemically reactive with, either adsorbent or resin.For ease in removal, volatile liquids, e.g., alcohol, water, ligroin,etc., are beneficial. The solvent can be selected to have just enoughsoftening effect on the resin so that good adhesion between the resinand adsorbent particles is obtained without separate treatment.Alternatively, the slurrying and coating vehicle will be removed and theresin particles then softened enough to insure adhesion to theassociated adsorbent particles and to the support, for example, byheating briefly to the softening point of the resin, typically to atemperature between and C. depending on the resin used. Alternatively amist or vapor of a solvent for the resin may be used. Combinations ofheat and solvent are useful and in some cases mechanical pressure can becombined with heat and/ or solvents to insure desired balance betweenporosity and abrasion resistance in the chromatographic layer.

For chromatographic sheet to be used with the acid charring technique, apreferred particulate binder is a polyolefin, particularly polyethyleneand polypropylene. Both high and low density polyolefins give goodresults. A polyolefin film, or olyolefin-coated paper or resinous filmof a different resin, provides an excellent base for such layers. Theresin binder is selected to be inert to the solvents to be used inchromatographic development. Although it is unnecessary to provide asubbing layer between the support and the chromatographic layer, suchsnubbings may be advantageous in improving adhesion of the binder to thesupport or in insuring good stripping where a temporary and readilyseparated support is desired. Good adherence to a support for use inthis system can also be obtained if the surface of the support isroughened by abrading it by applying a brush or abrasive to the surface.

The polymeric binders of our invention are mixed with the adsorbent inpowder or granular form. The polymers of the parent application, U.S.Ser. No. 450,362, of which this application is a continuation-in-part,can be used, according to the technique described in this application.These binders include hydrophilic polymers such as polyvinyl alcohol andgelatin-polyvinyl alcohol mixtures, thermosetting polymers such aspoly(vinyl acetal) resins and olefin polymers such as polyethylene andpolypropylene.

Many natural or synthetic thermoplastic or solventsoftenable resins canbe used in our layers. Examples of such resins include: polyvinylchloride, polyolefins, polystyrene, polymethacrylates, styrene-methylmethacrylate copolymers, polyvinylacetate, 'butadiene-styrenecopolymers, polyacrylates, and polyacrylic acid derivatives. Shellacandcolophony and other natural resins may also be used but care must betaken to see that nonsolvents are used both in the preparation andseparation stage to avoid destroying the porosity of the layer. Thesebinders are incorporated in their particular form. Excellent results arefor example obtained with powder, granules or pellets that pass througha U.S. Standard 325 mesh screen.

Alternatively the resinous binder may be used as an aqueous latex oremulsion of the resin. It is sometimes advantageous to employcombinations of two or more resins to enhance the porosity of the layerwhile improving the adhesion of the binder to the adsorbents and to thesupport.

Conventional coating methods and apparatus can conventionally be used tocoat the adsorbent-binder mixture onto the support. Thus doctor-blade,air-knife, roll-coating and hopper-coating techniques are applicable.

A test which demonstrates the improvement in thinlayer chromatographiclayers provided by our invention is one we designate as the Carnels HairBrush Test. This consists of brushing a chromatographic element with aCamels hair brush for 50 strokes under mechanically controlledconditions of pressure and rate of application. With a conventionalglass plate thin-layer chromatographic element complete removal of thematerial occurred with less than 50 strokes of the brush, frequentlywith the first or second stroke. Porous thin-layer chromatographicelements produced according to our invention showed no visible loss ofmaterial from the adsorbent layer after 50 strokes.

The invention can be readily understood with reference to the drawings.

FIG. 1 represents on an enlarged scale an elevational view looking atthe edge of a thin-layer chromatographic sheet produced according tothis invention wherein a particulate solid adsorbent and a particulateresinous binder 11 are coated on a polymeric film 13, the liquid vehicleremoved, and the adhesion of the resulting porous layer enhanced by heattreatment.

FIG. 2 is a cross-sectional view through the sheet of FIG. 1, but withmuch greater magnification, showing that the layer 11 is made up ofactive particles interspersed with resinous binder particles 17.

FIG. 3 is a graph illustrating the rate of solvent migration formethanol in centimeters per minute for a binderless chromatographiclayer A, representing the prior art, and for a layer B, representing ourinvention. The same adsorbent and concentration per unit area was usedin the two materials. a

The invention will 'be more clearly recognized by reference to thefollowing examples which are set forth to illustrate the invention, butnot to limit it. As shown by these examples, satisfactory results areobtained when the binder is present in the dispersion in a proportion offrom about 0.06 part per part by weight of the adsorbent (see ExampleXV) to about 1.6 parts per part by weight of the adsorbent (see ExampleVIII).

Example I 100 grams of neutral alumina, 65 grams of polyethylene powder(Microthene FNSlO, supplied by US. Industrial Chemicals, Div. ofNational Distillers and Chemicals Corp), and 115 ml. of ethyl alcoholwere thoroughly mixed together and the suspension coated on apolyethylene coated paper stock. After evaporating the alcohol, thecoating was heated for five minutes at 120 C., resulting in a porous,strongly adherent layer. A standard dye mixture was separated by thecoating after ten minutes elution with toluene.

The dye mixture used was obtained from Brinkmann Instruments, Inc.; itcontained 0.01 percent by weight of 4-dimethylaminoazo-benzene,indophenol, and Sudan Red G in benzene.

The alcohol was used merely to slurry the adsorbent and binder tofacilitate application of an even coating. The heat treatment bonded theresin and adsorbent particles into a coherent layer and bonded thebinder firmly to the support. The time and temperature of heating mustbe carefully controlled to insure that the polyolefin powder does notcoalesce and surround the adsorbent, but only softens at the surface toinsure adherence to joining particles thus preserving the porosityrequired for quick and efficient developer penetration.

Example II 36 grams of finely powdered cellulose, 24 grams ofpolyethylene powder, and 150 ml. of ethyl alcohol were slurried andcoated on polypropylene film. The coating was heated for five minutes at130 C. and then allowed to cool to room temperature. The resultingstrong porous chromatographic layer satisfactorily separated a mixtureof certified food colors after twenty minutes clution in an isopropanolethanol-water mixture.

Example IH grams of finely powdered silica gel, 40 grams of polyethylenepowder, 265 ml. of ethyl alcohol, and 140 ml. of water were thoroughlymixed together and coated on a polyethylene-coated paper. The coatingwas heated at C. for five minutes. The resulting abrasion-resistantchromatographic layer satisfactorily separated the standard Brinkmanntest dye mixture after ten minutes using toluene as the elutant.

Example IV 80 grams of finely powdered silica gel, 40 grams ofpolyethylene powder, 265 ml. of ethyl alcohol and ml. of water wereslurried and coated on a polypropylene film support. The coating washeated at 130 C. for five minutes. A strongly coherent chromatographiclayer resulted which satisfactorily separated the standard Brinkmanntest dye mixture after ten minutes using toluene as the elutant.

Example V 100 pounds of powdered nylon 11 polyamide adsorbent(Brinkmann, Instruments, Inc.), 65 pounds of finely powderedpolypropylene and 13 gallons of ethyl alcohol were thoroughly blendedtogether and coated on polyethylene film to obtain a dry thickness ofabout 40 mils. After heating the film for five minutes at 130 C., thecoating adhered firmly to the support and resisted abrasion. A sample ofthe film separated the Desaga test dye mixture after ten minutesdevelopment using methyl isobutyl ketone as a solvent.

Example VI 100 pounds of aluminum oxide (alumina AG7, Bio- RadLaboratories), 40 pounds of finely powdered polypropylene and 12 gallonsof ethyl alcohol were mixed together thoroughly and coated on apolypropylene coated paper to obtain a dry thickness of about 5 mils.The dried coating was then heated at 130 C. The chromatographic elementthus formed separated the standard Brinkmann test dye mixture, usingtoluene as the developing solvent in four minutes.

Example VII Example VIII 50 grams of finely powdered normalunsubstituted cellulose adsorbent (Cellulose MN300, BrinkmannInstruments, Inc.), 80 grams of polypropylene and 100 milliliters ofethyl alcohol were slurried and coated on clear polyethylene support.The coating was dried and heated for five minutes at 120 C. A sample ofthe coating was tested with a mixture of two food dyes as in ExampleVII. The dyes separated, using methanol as a development solvent, infour minutes.

Example IX grams of finely powdered silica gel, 100 grams of a finelypowdered styrene-methyl methacrylate copolymer, 470 ml. of ethyl alcoholwere thoroughly mixed together and coated on a polypropylene filmsupport. The coating was heated after solvent removal in an oven forfour minutes at 115 C. The resultant coating satisfactorily separatedthe standard test dye mixture after five minutes.

Example X 50 grams of finely powdered normal, unsubstituted, celluloseadsorbent, 70 grams of finely powdered polyethylene, 225 ml. of methylalcohol, and 150 ml. of isopropyl alcohol were mixed and coated on apolypropylene film support. The coating was cured after solvent removalby heating it in an oven for five minutes at 150 C. The resultantcoating satisfactorily separated the standard test dye mixture after tenminutes.

Example XI 130 grams of powdered nylon 11, 70 grams of finely powderedpolyacrylic acid, 225 ml. of benzene, and 150' ml. of toluene werethoroughly mixed together and coated on a polypropylene film support.The coating was heated after removal of the liquid vehicle in an ovenfor five minutes at 130 C. The resultant coating satisfactorilyseparated the standard test dye mixture after ten minutes.

Example XII 150 grams of finely powdered silica gel, 100 grams of finelypowdered polymethacrylate resin, 470 ml. of ethyl alcohol werethoroughly mixed together and coated on polypropylene-coated paper. Thecoating was dried and heated in an oven at 125 C. for eight minutes. Theresultant coating satisfactorily separated the standard test dye mixtureafter five minutes.

Example XIII 80 grams of finely powdered silica gel, 50 grams of finelypowdered polyvinyl chloride resin, 225 ml. of ethyl alcohol and 150 ml.of isopropyl alcohol were thoroughly mixed together and coated onpolypropylene-coated paper. The coating was dried and heated in an ovenat 125 C. for five minutes. The resultant coating satisfactorilyseparated the standard test dye mixture after five minutes.

Example XIV 80 grams of finely powdered silica gel, 40 grams ofpolyethylene powder, 265 ml. of ethyl alcohol, and 140 ml. of water werethoroughly mixed together and coated on an unsubbed polyethyleneterephthalate film. The coating was heated at 115 C. for five minutes,cooled to room temperature and stripped from the polyethyleneterephthalate film. This coating was equally as flexible as the previouscoatings and satisfactorily separated the standard dye mixture after tenminutes.

Example XV A slurry containing 150 grams of microcrystalline cellulose,9.4 grams of polyethylene powder, and 53 grams of 1,1,l-trichloroethanewas coated on a clear polypropylene film to a dry thickness of 10 mils.The solvent was then evaporated from the film leaving behind anadherent, porous chromatographic element. Using methanol as thedevelopment solvent, a mixture of two food dyes as described in ExampleVII was separated in four minutes. This solvent fusing technique inobtaining a porous layer is useful, but the appropriate solvent must befound to soften but not dissolve the polymeric-particles so that, ondrying, the adsorbent particles adhere to the polymer and the layerremains porous.

Example XVI 100 grams of neutral alumina, 65 grams of polyethylenepowder and 115 ml. of ethyl alcohol were thoroughly mixed together andthe suspension coated on a polypropylene-coated paper stock. Afterevaporating the alcohol, the coating was subjected to a mist spray of1,1,1-trichloroethane for two minutes. The coating was then dried. The

coating was tested as in Example XV and it was found to separate thefood dyes in four minutes.

Example XVII grams of finely powdered silica gel were added to a 40percent latex of polystyrene in water, and thoroughly mixed. The mixturewas coated on polyethylene coated paper and dried, the resultant coatingwas heated at 125 C. for five minutes, and then cooled to roomtemperature. The chromatographic element satisfactorily separated thestandard test dye mixture after five minutes.

Example XVIII Example XVII was repeated except that a 45 percent latexof polyvinylidene chloride in water was used. The result was essentiallythe same as Example XVII.

Example XIX grams of neutral alumina (325 mesh) and 65 grams ofpolyethylene powder (325 mesh) were slurried in ml. of ethyl alcohol andthe suspension coated on the polyethylene surface of a compositepolyolefin-polyester support, consisting of a 7 mil. thick layer ofpolyethylene laminated to a 7 mil. thick layer of a poly(ethyleneterephthalate). The alcohol was allowed to evaporate, and the coatingwas then cured for five minutes at C., resulting in a porous, stronglyadherent layer. The coating was tested as in Example I with equivalentgood results.

Example XX Naturally occurring or synthetic resins which become tackywhen contacted with water as a result of being watersoluble orwater-swellable (so-called water-soluble gums or mucilages) can be usedto form the binder particles for the practice of our invention. Theresulting chromatographic sheets can be used advantageously in thinlayer chromatography with organic solvent solutions. Thus, use can bemade of various starches, e.g., corn, potato, taroroot, locust beanstarches and the like, mucilages and water-soluble gums, such asgelatin, tragacanth, karaya, acacia, alginic acids and deviratives,hydroxyethylcellulose, carboxymethylcellulose,hydroxyethylcarboxymethylcellulose, poly(methacrylic acid), polyvinylalcohol, cellulose acetate phthalate and similar materials. These arehard, tough solid resinous materials in the dry state and can be groundto appropriate particle size for use in the practice of this invention.Cohesion of the resin particles and adhesion to the support and to theadsorbent particles can be effected by lightly wetting the surface. Forexample, granular powders of the adsorbent and a binderlike starch orgum arabic can be slurried in and coated from a non-solvent, such asStoddard solvent. After removal of the carrier liquid, the requiredadhesion can be obtained by treatment with a mist of warm water, orapplication of an aqueous solution of alcohol, e.g., 30% solution ofethanol in water, or the like.

Example XXI 10 grams of locust bean starch ground to 5-10 micronparticle size was thoroughly mixed with 85 g. of alumina of 1025 micronparticle size, slurried in 200 cc. ligroin and coated to a dry thicknessof 5 mils. on a PVA subbed cellulosic film. The ligroin was removed bydrying with forced air at 95 F. and the coating fixed by treatment witha spray of 30% solution of isopropanol in water. A coating of goodmechanical strength was obtained having a strong bond to the support. Itwas used in a chromatographic separation of a mixture of three dyes(sudan red, butter yellow, and indophenol blue) dissolved in benzene.

Example XXII 25 grams of granular hydroxyethylcellulose (averagediameter 510 microns) were intimately mixed with 250 g. of silica gel(average diameter 10-25 microns), slurried in 320 ml. of deodorizedkerosene and coated on a hydroxymethylcellulose-subbed cellulosic filmsupport. The liquid carrier was removed in a warm air dryer at 140 F.and the coating was stabilized by cooling the coating to 35 F. and thenpassing it through a chamber containing air saturated with water vaporat 120 F.

The water which condensed on the coating softened thehydroxyethylcellulose granules and the subbing sufliciently to promotegood adhesion to the support and to form a coating of adequatemechanical strength. The resulting sheet was used in chromatographicseparation of the dye mixture of Example XXI. Good separation wasobtained.

From the above description and examples, it is clear that the instantinvention bestows a heretofore unobtainable usefulness upon the art andscience of chromatography. The chromatographic sheets of the instantinvention can be precoated to exacting and reproducible standards undermass production conditions. Thereafter, the sheets can be readily storedor transported without elaborate precautions or fear of damage. Whenusing chromatographic sheets prepared according to the instantinvention, those in the art will have the benefit of substantially allof the advantages of the currently available glass plate binder-freethin-layer chromatographic elements wherein the adsorbent is merelydeposited on a glass plate support without a binder, while avoiding theserious disadvantages of such binder-free chromatographic elements. Thethinlayer sheets of the instant invention display chromatoggraphicactivity substantially equal to that of the binderfree elements withoutthe fragile powdering of the binderfree glass plates. Instead ofpreparing an adsorbent mixture, hand coating the adsorbent mixture ontoa bulky glass plate and drying the coated plate to render it useful,those practicing chromatography need only obtain a precoated thin-layerelement according to the instant invention and proceed with the desireddetermination or separation.

We claim:

1. A method of making a chromatographic element adapted for use inthin-layer chromatography, which comprises preparing a dispersionconsisting essentially of a particulate finely-dividedchromatographically-active adsorbent and a particulate finely-dividedresinous binder dispersed in a liquid dispersing medium, said binderbeing capable of being softened and made tacky by the action of heat ora solvent and said binder being present in said dispersion in aproportion of from about 0.06 to about 1.6 parts per part by weight ofsaid adsorbent; coating said dispersion on an inert support; removingsaid liquid dispersing medium from said coating; and rendering saidparticles of resinous binder in said coating soft and tacky to asuflicient extent that they adhere to particles which are adjacentthereto and form upon subsequent hardening a continuous, coherent,porous, chromatographicallyactive layer capable of use as aself-supporting layer.

2. The method as described in claim 1 additionally comprising the stepof stripping said porous chromatographically-active layer from saidsupport.

3. The method as described in claim 1 wherein said resinous binder is athermoplastic polymer and said particles of resinous binder are renderedsoft and tacky by heating to the softening point.

4. The method as described in claim 3 wherein said particles of resinousbinder are heated to a temperature 10 in the range between about C. andabout C.

5. The method as described in claim 1 wherein said resinous binder is aresin which becomes soft and tacky when contacted with a solvent andwherein said particles of resinous binder are rendered soft and tacky byapplyi g a solvent thereto.

6. The method as described in claim 5 wherein said liquid dispersingmedium is a partial solvent for said resinous binder and serves torender said particles of resinous binder soft and tacky.

7. The method as described in claim 1 wherein said inert support is apolyester.

8. The method as described in claim 7 wherein said polyester ispolyethylene terephthalate.

9. The method as described in claim 1 wherein said inert support is apolyolefin.

10. The method as described in claim 1 wherein said inert support ispolyolefin coated paper.

11. The method as described in claim 1 wherein said inert supportcomprises a layer of polyethylene terephthalate carrying thereon a layerof polyethylene.

12. The method as described in claim 1 wherein saidchromatographically-active adsorbent is selected from the groupconsisting of alumina, silica gel, kieselguhr, polyamide powder, andcellulose powder.

13. The method as described in claim 12 wherein said resinous binder isa polyolefin.

14. The method as described in claim 12 wherein said resinous binder ispolyethylene.

15. The method as described in claim 12 wherein said resinous binder ispolypropylene.

16. The method as described in claim 1 wherein the thickness of saidporous chromatographically-active layer is in the range from about 10 toabout 40 mils.

17. The method as described in claim 1 wherein said resinous binder ispresent in said dispersion in a proportion of from about 10 percent toabout 50 percent based on the volume of said adsorbent.

18. The method as described in claim 1 wherein said resinous binder isthe disperse phase of a resin latex.

19. A chromatographic element produced by the method of claim 1.

20. A chromatographic element produced by the method of claim 2.

References Cited UNITED STATES PATENTS 2,527,628 10/1950 Francis 264-122X 2,707,703 5/1955 Dorst 117-132 2,759,847 8/1956 Frost et a1. 117-1612,822,272 2/ 1958 Kosalek 9691 2,915,475 12/1959 Bugosh 2602.5 2,999,0169/1961 Beeber et al 96--75 3,161,519 12/1964 Alsup 117-138.8 3,303,0432/1967 Halpaap 117--33.5

WILLIAM D. MARTIN, Primary Examiner.

R. HUSAK, Assistant Examiner.

US. Cl. X.R.

